a²b + ab² = 70, 2ab = 20 হলে, a - b =?

প্রশ্ন: a²b + ab² = 70, 2ab = 20 হলে, a - b =?

সমাধান:
2ab = 20
⇒ ab = 20/2
⇒ ab = 10

a²b + ab² = 70
⇒ ab(a + b) = 70
⇒ 10(a + b) = 70
∴ a + b = 7

(a - b)² = (a + b)² - 4ab
= 7² - 4 × 10
= 49 - 40
= 9
∴ a - b = 3